Joan Smith: One abuser has been caught and jailed. There are thousands more

A year ago, on the Thai island of Phuket, I watched as out-of-work teenage prostitutes crowded the bars of a red light district. The sex trade was no more immune to the economic effects of the tsunami than the rest of the tourist industry, and the sheer number of girls in platform boots and halter-neck tops, hanging round in the hope of spotting a foreign man in search of sex, provided a bleak insight into the scale of prostitution in South-East Asia. Their voices, rising and falling as they chattered among themselves, could have come from a school outing.

These young women are part of a sinister migration, within their own countries and across borders, which exists solely to provide cheap sex for predatory foreign men. Some are after women, others seek boys or under-age girls; when Gary Glitter was arrested on sex offences in the Vietnamese resort of Vung Tou last year, his victims included a 10-year-old girl who had been transported 190 miles from home by her aunt to have sex with the former rock star. His other victim, who was 11 at the time, is also believed to have been pimped by a relative.

Glitter, whose real name is Paul Gadd, protested his innocence to the end, blaming his conviction on a conspiracy as he was sentenced to three years in prison last week. The judge concluded that Gadd understood he had "a sickness", although the former glam rocker did not show much evidence of it. Nevertheless, his behaviour exhibits a familiar pattern; since being imprisoned for possessing child pornography in the UK in 1999, he has travelled the world, turning up in destinations popular with men looking for sex with children.

In 2002 he was expelled from Cambodia after being held for three nights on suspicion of committing sex offences. Like Thailand and Vietnam, Cambodia has a huge problem with foreign sex tourists, most of whom do not share Glitter's level of visibility. According to World Vision International, which published a report on the child sex trade in Cambodia, foreign men are prepared to pay up to $800 for sex with an under-age virgin; after a couple of weeks, the price drops to between $15 and $30. One young girl told the researchers she was paid $1.20. Children involved in the sex trade identified "French" men as the largest group of customers: the word is commonly used by street children to mean European.

This is the harsh reality of prostitution in a globalised world, where growing numbers of men from affluent countries collude with pimps and sex traffickers in foreign tourist resorts. It is an international problem, which governments, including our own, have been slow to address. According to campaigners, there have been only three successful prosecutions in this country of British men for abusing children abroad under a law that came into effect in May 2004. In January, Alexander Kilpatrick, a 56-year-old father of two, became the first person to be jailed under the legislation, after making trips to Africa to abuse poor children.

Relaxing laws on commercial sex at home makes the situation worse. Australia and the Netherlands, which have some legalised brothels, have the highest number of sex tourists per capita; if men can buy sex at home with impunity, they are more likely to do so abroad.

Glitter cut an unpleasant figure in court last week, unrepentant and showing off for journalists. There are thousands more like him. Whatever the age of the victims, wherever they live, prostitution is a form of abuse, based on the repugnant notion that women and children are commodities to be bought and sold.